Switch to herald for releasing

[carbolymer]

Changelog

- description: |
    Switch to herald for releasing
# uncomment types applicable to the change:
  type:
  # - feature        # introduces a new feature
  # - breaking       # the API has changed in a breaking way
  # - compatible     # the API has changed but is non-breaking
  # - optimisation   # measurable performance improvements
  # - refactoring    # QoL changes
  # - bugfix         # fixes a defect
  # - test           # fixes/modifies tests
   - maintenance    # not directly related to the code
  # - release        # related to a new release preparation
  # - documentation  # change in code docs, haddocks...

Context

Switch to herald for releasing. This PR is a copy of changes from IntersectMBO/cardano-api#1164

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. See Running tests for more details
• Self-reviewed the diff

[Copilot]

Pull request overview

This PR migrates the repository’s changelog/release process to herald, replacing the previous PR-description-based changelog check with fragment-based validation and adding a manual release workflow.

Changes:

• Add .herald.yml to define change kinds and the cardano-cli project metadata for herald.
• Replace the existing “PR changelog” GitHub Action with a herald fragment validation workflow.
• Update the PR template and add a .changes/_TEMPLATE.yml to guide contributors toward fragment-based changelogs.
• Add a new workflow_dispatch-driven release workflow that invokes herald-release.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
.herald.yml	Introduces herald configuration (kinds, bumps, project paths).
.github/workflows/release.yml	Adds a manual release workflow using herald-release.
.github/workflows/check-pr-changelog.yml	Replaces PR-description changelog checking with herald validation.
.github/PULL_REQUEST_TEMPLATE.md	Updates contributor guidance to require .changes/ fragments and how to create them.
.changes/_TEMPLATE.yml	Adds a fragment template for contributors (ignored by herald due to _ prefix).

Comments suppressed due to low confidence (1)

.github/workflows/check-pr-changelog.yml:33

• The PR template/checklist says every PR needs a changelog fragment in .changes/, but this required check currently runs herald-validate with pr: false, so it won’t enforce that PRs actually add a fragment. Consider enabling PR-level validation (or adjusting the template text) so CI and contributor guidance don’t diverge.

      # TODO: enable --pr check after backfilling existing PRs with fragments
      - uses: input-output-hk/cardano-dev/actions/herald-validate@herald-validate-0.0.1.0
        with:
          pr: false

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